Dendritic Cell Migration and Maturation
Amongst the distinctive features of dendritic cells are their migratory properties. Migration has been studied to a large extent in skin. During contact sensitivity, dendritic cells (Langerhans cells) are noted in the afferent lymph (Lens et al., 1983; Silberberg-Sinakin et al., 1976) and in the draining lymph node (Kripke et al., 1990; Macatonia et al., 1987). Following skin transplantation, dendritic cells leave the epidermis and undergo changes that include increased expression of MHC class II (Larsen et al., 1990). Since dendritic cells are known to gain access to afferent lymphatics (Knight et al., 1982; Lens et al., 1983; Pugh et al., 1983; Rhodes et al., 1989), the migration of these potent antigen presenting cells into the lymph and then to the draining lymph node, may account for the need for intact, cutaneous afferent lymphatics during the primary response to transplants (Barker and Billingham, 1968) and contact allergens (Frey & Wenk, 1957) in situ. In recall or delayed type hypersensitivity reactions, dendritic cells also are juxtaposed to the infiltrates of dermal mononuclear cells (Kaplan et al., 1987).
When dendritic cells are pulsed with antigens ex vivo and are injected into mice, CD4.sup.+ T cells are primed in the draining lymphoid organs (Inaba et al., 1990; Liu and MacPherson, 1993; Sornasse et al., 1992). Austyn et al. showed that dendritic cells, when placed into the blood stream or paws of mice, migrate to the T cell areas in the draining lymphoid tissue, i.e., spleen and lymph node respectively (Austyn et al., 1988). If antigens are deposited intramuscularly, the dendritic cells from the corresponding afferent lymphatics carry that antigen in a form stimulatory for T cells (Bujdoso et al., 1989). Therefore, the migratory properties of dendritic cells likely interface with their antigen presenting functions to sensitize T cells in situ.